Please see my most recent response to Predrag B.
The presciption you show above went off without a hitch (Thanks), but
it appears upon creating a new vm with the newly installed vbox
GUI. that it may only be capable of creating 32 bit vms/.
Do you see something like that?

Nope! I see both 32 and 64 bit in the list (will attach picture, if it
survives).